MONDAY, Aug. 11, 2014 (HealthDay News) -- Chronic diseases that can increase a person's risk of heart attack or stroke appear to hit women and blacks the hardest, a new population-based study found.

Diabetes and high blood pressure in particular, contribute to an ongoing gender and race gap in heart disease risk, researchers report online on Aug. 11 in the journal Circulation.

"These findings could support the idea that when a woman or a black patient has these risk factors, they tend to be not as recognized or well-controlled, because they aren't as aggressively treated," said Dr. Susan Cheng, a specialist in cardiovascular medicine at Brigham and Women's Hospital in Boston.

Researchers studied more than 13,500 Americans between 1987 and 1998 to determine their population attributable risk -- a measure that considers how common a risk factor is and by how much that factor raises the chance of future heart disease.

The study evaluated the combined and individual impact of five major risk factors for heart disease -- high cholesterol, smoking, high blood pressure, obesity and diabetes.

The combined risk from all five factors remained the same in blacks over a 10-year period, causing a steady 67 percent increased risk of heart disease. At the same time, the combined risk fell for whites, dropping from 56 percent to 48 percent.

Combined heart disease risk fell for women during the same 10 years, decreasing from 68 percent increased risk to 58 percent.

But their risk still remained higher than that of men, whose combined risk decreased from 51 percent to 48 percent during the study period.

This difference in risk could be due to the fact that heart disease has typically been considered a disease of white men, and doctors have not tackled contributing factors as much when they crop up in women or blacks, Cheng said.

Biology also may play a role, said Dr. Nieca Goldberg, medical director of the Women's Heart Program at NYU Langone Medical Center.

"It may mean that these certain risk factors confer a greater risk in these people, for different reasons," said Goldberg. For example, studies have shown that women's heart health is more dramatically affected by prediabetes than that of men.

Diabetes and high blood pressure emerged as the two factors that continue to drive up the risk of heart attack and stroke, particularly in women and blacks.

"The overall impact of diabetes is pretty major, and it's more significant as a major contributor as time goes on, the obesity epidemic continues, and we get better at controlling other risk factors," Cheng said. "We are concerned it's going to be the risk factor that explodes over the next few decades."

High blood pressure also persists as a major risk factor that disproportionately affects women and blacks. It increases women's risk of heart disease 32 percent compared with 19 percent for men, and increases blacks' heart health risk by 36 percent versus 21 percent for whites.

"The relative contribution of high blood pressure to overall risk for heart disease is much higher in blacks than whites, and has historically been higher in women than men," Cheng said. "This is something we should be able to get under control, but for some reason we haven't been able to make the sort of impact we've made with cholesterol."

Both smoking and high cholesterol have decreased as risk factors for heart disease.

Smoking risk dropped slightly from 15 percent to 13 percent for all Americans. Fewer people are smoking, Cheng said, but those who still smoke face a higher average risk of heart disease than smokers did 20 years ago.

"One theory is that the people who still smoke are genetically more predisposed to being addicted to nicotine, and so they smoke more cigarettes on hand than smokers did 20 years ago," she said.

Cholesterol-lowering statin drugs have allowed huge inroads against high cholesterol as a heart risk factor, chopping the risk in half for all Americans. High cholesterol now causes 9 percent increased risk, compared with 18 percent a decade earlier.

Obesity contributes a relatively low amount of increased risk, around 6 percent. The researchers said that obesity's effects may grow in later life, and also might boost the risk of other factors like diabetes.

These findings should prompt doctors to treat risk factors more aggressively for heart disease that appear in women and blacks, Goldberg said.

"It's really important for us to address all the risk factors, but also be aware that women and African-Americans are really susceptible for high risk of heart disease with the presence of diabetes or high blood pressure," she said.